1. Field of the Invention
An aspect of the present invention relates to a sheet feed cassette. More particularly, it relates to a sheet feed cassette capable of mounting sheets of a plurality of sizes, and an image forming apparatus using the same.
2. Description of the Related Art
In recent years, the reduction of size of an image forming apparatus has proceeded. Accordingly, a sheet feed cassette to be mounted in an image forming apparatus main body has been also reduced in size. However, the size of the sheet to be used remains unchanged. Therefore, according to a size reduction of the sheet feed cassette, the size of the mountable sheet is limited. Thus, there are proposed a system in which an exclusive sheet feed cassette for small size sheets, large size sheets, or the like is selected for each size of sheets to be used; a system in which the sheet feed cassette is made extractable to support from small size to large size sheets; and the like (e.g., see JP-A-9-110184).
Also, some of the sheet feed cassettes each projecting from an image forming apparatus main body include a top side cover attached thereon.
However, in the case of the system in which an exclusive sheet feed cassette is selected for each size of the sheets to be used, the sheet feed cassettes are required to be changed for every size of sheets. Therefore, the operation is troublesome. Further, a plurality of the sheet feed cassettes are required to be prepared, resulting in a correspondingly higher cost. In addition, additional space such as the storage site for the sheet feed cassettes not in use also becomes necessary. Thus, the operability is not good.
As compared with that, with the systems in which the sheet feed cassette is made extractable, one cassette can support sheets of a plurality of sizes. Therefore, the system is excellent in general versatility. However, there are many systems complicated in structure, systems unstable in positioning of sheets, or other systems.
For example, in JP-A-9-110184, an extractable sheet feed cassette includes a main container and a sub container. One side of the main container to be mounted in an image forming apparatus is formed in a double structure of a top plate and a bottom plate so as to have a space therebetween. And, the sub container is slidably inserted into the space between the top plate and the bottom plate. In the cassette, the main container is configured in a double structure for ensuring the rigidity. However, with such a configuration the structure is complicated, and further the cost also increases. Also, when the sub container is extracted or retracted, the reliability is poor because the locking mechanism for holding the sub container at a desirable position is formed of an elastic member formed on the sub container. Thus, a deviation tends to occur in the positional relationship between the main container and the sub container during attachment and detachment, or the like of the sheet feed cassette. As a result, a deviation occurs at the sheet feed position, and malfunctions, such as sheet feed jam and erroneous detection of the sheet size, occur. Thus, the operability is not good.
In the case of the extractable cassette, the top side cover is necessary when the cassette is extracted outside the image forming apparatus. However, it is not necessary when the cassette is retracted. Therefore, there has been a demand for the one which is easy to attach or detach, and is rotatable.